1. Field of the Invention
The present invention relates to a multi-speed transmission wherein a plurality of drive gears and a plurality of driven gears are supported, in the state of being in constant mesh on a gear speed basis, respectively on gear shafts parallel to each other, and particularly to a shift drive mechanism.
2. Description of Background Art
In the multi-speed transmission of the constant-mesh type, one group of gears of the drive gears and the driven gears are fixed on the gear shaft, the other group of gears are rotatably borne on the gear shaft, and one of the rotatable gears which is engaged with the gear shaft is switched over by an engagement switch-over mechanism, thereby performing a shift.
In regard of a shift drive mechanism by which an engagement switch-over mechanism for switching over engaging means provided between a plurality of gears and a gear shaft so as to make engagement therebetween is driven to perform a shift, a configuration wherein a shift rod disposed along the center axis of an inner cavity of a gear shaft moves cam rods being put in slidable contact with the inner peripheral surface of the inner cavity of the gear shaft so as to be movable in the axial direction, and the cam rods drive the engaging means so as to perform a shift. See, for example, Japanese Patent Application No. 2008-093703 previously applied by the same applicant as the applicant of the present invention.
The shift drive mechanism for a multi-speed transmission disclosed in Japanese Patent Application No. 2008-093703 has a configuration in which a shift pin is radially projectingly provided on an operating member mounted to an end portion of the shift rod through a bearing, an end portion of the shift pin is slidably engaged with a shift guide groove formed in an outer peripheral surface of a shift drum, and the shift pin is moved in the axial direction while being guided by the shift guide groove attendant on turning of the shift drum, whereby the shift rod is moved through the function of the operating member. In this configuration, a shift is performed by the above-mentioned engagement switch-over mechanism which is operated by movement of the shift rod.
The moving position of the shift rod for setting of each gear speed is a substantially fixed position, and, in order that the shift rod is stably maintained at a desired fixed position, a Geneva stop mechanism as an intermittent drive mechanism for turning the shift drum intermittently is provided in the system disclosed in Japanese Patent Application No. 2008-093703.
Since the intermittent drive mechanism which is complicated and bulky is provided at an end portion, protruding from an end portion of the driven gear shaft, of the shift rod inserted in the inner cavity of the driven gear shaft along the center axis, the multi-speed transmission as a whole is large in weight and high in cost.